The objectives of this research plan are as follows: 1. Evaluate the functional significance of collateral circulation in the rat and dog kidney during complete and partial renal artery occlusion. 2. Determine tubular permeability to insulin in dogs and rats after partial and complete arterial occlusion and correlate permeability with ultrastructural changes in tubular cells and intercellular tight junction. 3. Determine the biochemical effects of varying durations of partial and complete arterial occlusion, with emphasis on membrane functions. Correlate biochemical findings with anatomical observations. 4. Determine the effects on proximal tubular brush border of renal ischemia of varying duration. If brush border is destroyed by brief ischemica which does not cause irreversible cell damage, study the function of proximal tubules without normal brush borders. 5. Study the mechanism of action in the renal microcirculation by which mannitol alters renal hemodynamics, using the Munich rat: (a) under control conditions, (b) after one hour of total arterial occlusion, (c) after three hours of partial arterial occlusion, (d) during partial arterial constriction. Evaluate anatomical changes in the microcirculation induced by ischemia and by mannitol. 6. Define RBF and intrarenal distribution of RBF in both anesthetized and unanesthetized dogs during hemorrhagic hypotension and renal arterial clamping. Explore the possible roles of the sympathetic nervous system, angiotensin and prostaglandins in any changes in flow distribution or in any differences between hemorrhage and clamping.